I just used a piece of cardboard about a foot long and 4 inches wide, wrapped masking tape to thicken it up, left the center flexible. I taped the bladder to it fed it through and when I I got to the wing tip I folded the cardboard in half and pulled it out. Bladder was in and I did not have any twist. Oh, and I did not use any string. Works pretty well.

Another good thing is, that you can easier put the bladder back ALONE with your method !

With a string you have to have lots of space (meaning doing it outside only - where it might rain the very day...), and find something the string can be put around and back to you, while you hold the other end and/or feed the bladder into the zip.

So if you dont have a girl/boyfriend to help - it should be easier this way, also inside the house.

I've seen several bladders explode because of a twisted front bladder - sometimes if only a half twist it holds for some time on the water, and then suddenly, BANG one day
Although - a half twist is YOUR OWN FAULT of course, if it happens after a bladder change, as you can see if the bladder tip is turned around or not (usually text on one side only).

Dont know if this can happen today, where we have more pressure in the kites than earlier - but I think it can

A full twist can happen quite easy though, if you are alone when reinserting and using a string
So good idea